The analytical capabilities of the gas chromatograph and the mass spectrometer are greatly enhanced when the two instruments are combined and one such combination is described. A helium separator is used to remove preferentially the chromatograph carrier gas before reaching the mass spectrometer, so obtaining higher concentrations of the sample. The mass spectrometer used is a small 60° sector field instrument which can produce mass spectra over the range 26-400 a.m.u. in 1/10 second. This scan rate permits direct analysis of chromatograph eluent peaks as they appear. The combined instrument has been applied to such problems as food flavour research and oil degradation investigations.